【作者】 骆进；

【导师】 项伟；

【作者基本信息】 中国地质大学 ， 岩土工程， 2010， 硕士

【摘要】 湿陷性是黄土最重要的性质之一。据统计我国湿陷性黄土分布面积为38万平方公里,占我国黄土地区总面积的60%以上。由于黄土具有湿陷性,常给黄土地区的工程建设带来不可言喻的祸患。众多研究表明黄土的湿陷变形是由于黄土连结弱化导致的,从含水量的角度讲非饱和黄土与浸水条件下的饱和黄土湿陷变形都是存在的,且此方面的研究成果比较丰富。然而自然界中降雨经常沿黄土的节理直接入渗到坡体内部,形成力场和渗流场耦合情况下的渗透变形,这一变形也叫潜蚀湿陷。本文基于前人的研究成果,通过文献阅读对黄土的基本理论做出了一些总结。重点对黄土的物质组成、结构特征和湿陷性进行了介绍。黄土的物质组成主要包括：粗颗粒、粘土颗粒、水溶盐三大类物质；黄土的结构形式有多种说法,本文综合性的从粗颗粒形态、颗粒的连接方式、孔隙和胶结物几个方面对黄土的结构做出了阐述；在湿陷性方面,总结了前人的研究成果,从黄土湿陷机理和各种假说做出了相应的分析。通过资料收集和野外调查,弄清了研究区地质环境背景。研究区第四纪地层出露有全新统、上更新统、中更新统。前第四纪地层出露有第三系上新统三趾马红土和中生界三叠系上统瓦窑堡组。区内地质构造简单,大的断裂及褶曲不发育,仅在局部地段分布一些小的断层及褶曲。地震烈度小于6度。区内地表水体主要是秀延河、寒沙石水库及沿省道205展布的季节性河沟及部分侵蚀冲沟渗出水。地下水按含水介质、赋存条件和水力特征,分为松散岩类孔隙水和碎屑岩类裂隙水。经过野外实地踏勘、地质资料查询和室内试验证明了研究区的黄土具有一定代表性。同时,通过对试样的颗粒级配、细颗粒含量的分析证明了研究区的黄土基本符合潜蚀湿陷发生的一般条件。通过对南55渗透仪的改装,配合空压机的水压力驱动系统使力场和渗流场耦合的试验条件得以实现。选择改装南55渗透仪主要是考虑该仪器在土体渗透系数的测定上已经比较成熟,在固结仪上加压也比较方便。本文试验及结果处理分三步：首先,对土样进行室内湿陷性试验,通过试验结果分析选择了1、2号样为湿陷样代表,5、6号样为非湿陷样代表进行渗透变形试验。重塑土采用干密度控制法,本文重塑土样干密度主要有：1.3g／cm3、1.4g／cm3、1.5g/cm3、1.6g／cm3、1.7g／cm3五种类型；对试验所得的数据进行处理,做出了两种试验方案下的渗透变形曲线。通过对渗透变形曲线的分析,得出了不同干密度的重塑性黄土和原状黄土的渗透变形规律。其次,收集原状样的渗出液并进行电导率测试,根据前人关于易溶盐含量与电导率转换的研究成果,提出一个计算黄土易溶盐溶蚀率的式子。运用易溶盐溶蚀率的式子对渗出液的电导率进行处理,得到了易溶盐溶蚀的一些规律。最后,通过对渗透变形试验前后的原状样和渗透样分别进行微观结构测试,并对SEM图像进行了一些微观结构物理指标的统计,综合性的分析了渗透变形发生的机理。本文主要研究成果如下：1.提出了南-55渗透仪改装成渗透固结仪的想法及应满足的试验要求,成功的改装了南-55渗透仪,经过调试证明了改装的渗透固结仪满足试验的要求。2.通过定压力试验及结果分析：重塑土的干密度小于1.4g/cm3时黄土渗透变形与渗透水压呈二次函数关系,当于密度大于1.5g/cm3时黄土渗透变形与渗透水压则呈线性关系；而原状黄土中湿陷性黄土的渗透变形量要远远大于非湿陷黄土。3.通过定水头变压试验及结果分析：干密度一定时,渗透变形量与渗透水压呈正相关；渗透水压一定时,干密度和渗透变形量呈负相关。4.通过重塑土样的定压力试验和定水头变压试验结果横向对比分析：两种类型的试验变形量在1.4g/cm3和1.5g/cm3之间均存在一个转折点,转折点上下的变形轨迹有着很大的差别,大体为：密度小于1.4g/cm3时黄土渗透变形与渗透水压呈非线性数关系,密度大于1.5g/cm3时黄土渗透变形与渗透水压呈线性关系。5.根据前人关于易溶盐含量与电导率转换的研究成果,笔者提出一个计算黄土易溶盐溶蚀率的式子：v=((ξ×Q).V)/t(单位g/min)。这样可以避免易溶盐测试的繁琐的试验的过程,更方便的计算易溶盐的溶蚀量,以达到更便捷和全面的分析和评价黄土易溶盐溶蚀的目的。6.将收集的原状样的渗出液进行电导率测试,利用以上公式进行处理可知：电导率与渗透水压呈负相关,湿陷性黄土和非湿陷性黄土的易溶盐溶蚀率均随渗透水压的增大而增大；相同条件下,湿陷性黄土的易溶盐溶蚀率要大于非湿陷性黄土；溶蚀率与竖向荷载有一定关系,在湿陷性黄土中溶蚀率随着竖向荷载增大而减小,而非湿陷性黄土此种特征表现不明显。7.对渗透变形试验前后的黄土试样分别进行微观结构试验,通过对微观结构中各项指标进行统计,结合土体抗渗强度的结构特性要求对其发生渗透变形的必要条件进行分析,得出试验用两种土样均符合渗透变形发生的基本条件,其中湿陷性土样的指标D/d0为2.8,比较接近渗透变形发生的最优比例2.5。8.通过对黄土渗透变形前后孔隙长轴方位角做出长轴节理玫瑰花图,可知渗透变形后孔隙排列方式发生了改变,变得更具定向性。最后,综合性的分析了以上试验及结果,得出了黄土渗透变形是黄土化学潜蚀和机械潜蚀的结合。渗透水流浸入土体溶蚀了黄土中的水溶盐,弱化了黄土的胶结强度,同时机械潜蚀带走了起胶结作用的粘土颗粒,进一步破坏了黄土的胶结作用,加剧了黄土潜蚀湿陷的发生。更多还原

【Abstract】 Collapsibility is one of most important characteristic of Loess. There are 380 square kilometers loess area in China, which accounted for over 60% of China’s loess area according to report. Becaμse of the special characteristic series of unpredictable disease of the constructions often occurred in loess area. Lots of research results indicated that weak junction of particles is the main factor contribute to collapsibility of loess.Collapsibility of unsaturated and saturated soil is existed in the term of water content, and lots of researches have testified such phenomenon. However, when the rain permeates into the body of soil along with the joint of loess, collapsible seepage deformation of loess occurred under the coupling between stress and seepage.This paper based on exist research results, theoretical information of loess was presented after the reading of literature.Then introduction of loess about meaning, classification, composition, physical characteristic, structural characteristic etc will be presented. The introduction mainly contained three aspects as follow:Firstly, there are mainly three types of mass consist of loess: coarse particles, clay, water soluble salts. Secondly, structural types will be expound by shape of coarse particles, connection type of particles, porosity and cement in this paper. Thirdly, analysis of collapsibility was carried out based on former research results, mechanicals of collapsibility and kinds of hypothesis.Background of geological environment of research area was clarified by analysis collected data and field investigation. The Quaternary strata exposed are Holocene, Upper Pleistocene, Middle Pleistocene. Pre-Quaternary strata exposed are Pliocene Tertiary Hipparion clay and Triassic Mesozoic Wayaobao the EC group. The geological structure of the study area is simple, major fault and fold is not development, only distribution of some minor faults and folding in the local sites.Seismic intensity is less than 6 degrees. The main surface water are Xiu Yan river, cold sand reservoir and the seasonal rivers and part of water seeping erosion gully along the provincial highway 205.According to water-bearing media, storage conditions and hydraulic characteristics, groundwater can be classfied into loose rocks pore water and clastic rock fissure water category. The fact that the loess of research area was representatively could be testified according to the results of investigation and inner door experiment. Meanwhile, the requests of collapsible seepage deformation happed also testified by analysis of grain composition and clay content.Coupling between stress and seepage will be achieved by remodel the permeameter and by apply the water pressure system. The reason of choose remodel permeameter is that the maturity of measure in permeability coefficient and convenient in apply vertical load at consolidometer. In this paper the experiment and the results handling can classified into 3 phases:Firstly, inner door experiment for collapsibility of loess and relevant analysis was carried out, NO.1 and NO.2 were selected for respective of collapsibility, NO.5 and NO.6 were selected for respective of uncollapsibility after the analysis of experiment results. Remoulded soil controlled by dry density there are 5 types remoulded soil in this paper:1.3g/cm3、1.4g/cm3、1.5g/cm3、1.6g/cm3、1.7g/cm3, the curve of seepage deformation was drew after processing test data and discipline of seepage deformation was acquired after analysis of the curve.Secondly, collect the exudate of undisturbed soil during seepage experiment and measure the conductivity of exudate. A function of soluble salt ration was proposed according to existent research results of covert between soluble salt and conductivity. Handing the conductivity of exudate by the function then the law of soluble salt dissolution can be achieved. Finally, test of microstructure was carried out byμsed the sample before and after experiment of seepage deformation. Statistics about the physical index of microstructure by SEM photo was also done.Then, mechanics of seepage deformation was presented. The main research results of this paper as follow:1.The idea and relevant requests of remodel the Infiltration devices into Infiltration-consolidation devices was proposed. Relevant requests of Infiltration-consolidation can be fit by debugging.2.After constant load pressure tests and analysis of relevant results:The relation between seepage deformation and water pressure was presented as quadratic function when the density of the remodel soil less than 1.4g/cm3,and the linear was presented when the density bigger than 1.5g/cm3.The seepage deformation of collapsible sample was much bigger than the uncollapsible samples in undisturbed soil.3.After constant water pressure tests and analysis of relevant results:The correlation between seepage deformation and water pressure was positive at the conditions of constant dry density, negative correlation was present between seepage deformation and dry density at the conditions of constant water pressure.4.After the comparison between constant load pressure tests and constant water pressure tests: There is a turning point exist among 1.4g/cm3 and 1.5g/cm3,and the principle of deformation was severe vary at two side of this point. The mainly principles was:nonlinear relation was presented when the dry density was less than 1.4g/cm3,and the linear was presented when the density bigger than 1.5g/cm3.5.A function of soluble salt ration was proposed according to the exist research results of exchange between soluble salt and conductivity:v=((ξ×Q).V)/t (unit:g/min).Byμse this function more convenient in calculator and more speedy in analysis or assessment of the quantity of soluble salt would be achieved.6.Conductivity tests was implemented at the collected liquid of undisturbed soil, handing the results by the function proposed above, then the principles was detected:The correlation between and conductivity and water pressure was negative, with the increase of water pressure the ration of soluble salt increase too.The ratio of undisturbed sample was much bigger than disturbed sample. With the increased of vertical load the ratio of soluble salt was reduced.Ratio of soluble salt of undisturbed soil was larger than disturbed soil at the same conditions.7.Microstructure tests was implemented byμsed the sample before and after collapsible tests. Requirements of seepage deformation occurred was analyzed by analysis of microstructure index and structure property of sample. Then the requirements of seepage deformation was acquired, the index D/do was 2.8 in collapsible samples which was nearly close to the best ratio of seepage deformation occurred8.After measuring the long axis of porosity the rose diagram can be draw, we can see from the diagram that the arrangement of porosity was changed after collapsibility its become much more orient.Finally,after comprehensive analysis of above experiment and relevant results, The reason of seepage deformation was the combine chemical erode and mechanical erode was presented. Water permeated in the soil and then soluble salt was eroded, which weak the cement of loess. At the same time, the clay glued particles was took away by mechanical erode, which deeply destroyed the structure of loess.Then collapsible seepage deformation was occurred.更多还原